1. Field of the Invention
The present invention relates to an optical fiber telecommunication cable, in particular for connecting user telecommunication installations to switching and routing centers.
2. Description of the Related Art
For reasons of economy, the connection of user installations by optical fibers is carried out at the request of the users, use being made of individual microconduits or miniconduits that are allocated to respective users. The telecommunication operator managing these user connection lines connects only those users that request this connection. This is more economical than prior precabling systems that include potentially “connectable” user installations without being certain which users would be interested in having a connecting line employing one or more optical fibers.
In a prior art user line concentration embodiment shown in FIG. 1, individual microconduits or miniconduits MCO dedicated respectively to users or groups of users are contained together within an existing conduit CD in order to reduce the civil engineering cost of installing user lines. Each microconduit or miniconduit MCO contains a microcable or minicable MCA dedicated to a user or a group of users and installed at the request of the user or the group of users. FIG. 1 shows two microcables or minicables and five microconduits or miniconduits MCO that are awaiting the installation of microcables or minicables.
A sheath G may clothe the assembly of microconduits or miniconduits MCO to constitute a “multimicroconduit” or “multiminiconduit” system, as shown in FIG. 1.
The microconduits typically have an inside diameter lying between 3 mm and 5 mm and an outside diameter lying between 5 mm and 8 mm and each comprises a microcable having an outside diameter of less than or equal to 3 mm, generally from 0.8 mm to 2 mm. Miniconduits and minicables have larger sections than microconduits and microcables. Miniconduits typically have an inside diameter lying between 6 mm and 12 mm and an outside diameter lying between 8 mm and 15 mm. Minicables have an outside diameter less than or equal to 11 mm, generally from 3 mm to 10 mm.
Because of the small sections of microcables, minicables, microconduits and miniconduits, each microcable in a microconduit or each minicable in a miniconduit is generally installed by a blowing or floating technique.
FIG. 2 shows diagrammatically the installation of a microcable or minicable MCA in a microconduit or miniconduit MCO using a blowing technique. The microcable or minicable MCA is unwound from a drum R around which the microcable or minicable is loosely wound in the form of a spool and which turns freely about the axis of a support SU placed on the ground. A free end of the microcable or minicable MCA is fitted with a core OB having a section substantially smaller than that of the microconduit or miniconduit MCO. The microcable or minicable is paid out from the drum R and pulled longitudinally along the microconduit or miniconduit by the core, in the direction of the arrow FT, by virtue of the thrust exerted on the rear of the core OB by a flow of compressed air AC.
FIG. 3 shows diagrammatically the installation of a microcable or minicable MCA in a microconduit or a miniconduit MCO using a floating technique. The minicable or microcable is paid out from a drum R mounted freely on a support SU resting on the ground by two rollers RO turning in opposite directions that push the microcable or minicable MCA into the microconduit or miniconduit MCO. A fluid FL such as air or water injected under pressure into the microconduit or the miniconduit MCO allows the microcable or minicable to “float” in the microconduit or miniconduit at the same time as being pushed by the two rollers RO. This floating technique applies much lower mechanical stresses to the microcable or minicable than the blowing method shown in FIG. 2.
Optical fiber telecommunication minicables and microcables respectively intended to be installed in miniconduits and microconduits comprise a thin retaining sheath that offers a relatively high coefficient of friction in respect of hard plastic material microconduits and miniconduits. Consequently the retaining sheath has braking effect relative to the forward movement of the microcable or minicable in the microconduit or miniconduit by blowing in compressed air or by flotation in a fluid and pushing by rollers.
Moreover, the retaining sheath offers a low stiffness which causes the microcable or minicable to buckle, an effect which becomes more accentuated as the length of the microconduit or miniconduit increases. Any exaggerated pushing of the retaining sheath against the wall of the microconduit or miniconduit brakes forward movement of the microcable or minicable.